Then he realized he was being asked to play the Colonel, an iron-fisted, ruthless soldier brought in to tamp down the now hyper-intelligent apes waging war with mankind.

The 55-year-old actor admits he was a bit chagrined. “I tried anything and everything to get them to come around, but they told me I was playing a human,” he explains, tongue in cheek, during a recent chat at a posh Manhattan hotel. Dressed in a blue T-shirt and hoodie, he’s approachable and irreverent. “I kept insisting I wanted to be an ape. We volleyed it back and forth; but it was human that won out in the end.”

A longtime vegan and animal lover, it’s fair to say that playing the Colonel waging war on chimpanzees, many of whom came from scientific testing labs, is counter-casting for Harrelson.

War for the Planet of the Apes is the third film in the rebooted film franchise that kicked off with 2011’s Rise of the Planet of the Apes, in which baby ape Caesar is taken in and raised by humans after his mother, a lab chimp, is killed, and follows Dawn of the Planet of the Apes, about the intensifying antagonism between apes (now with super-intelligence, thanks to the ALZ-113 virus) and humans, which is about to become an all-out war.

As War for the Planet of the Apes begins, apes and humans are two years into their fight, the apes hold the upper hand in the woods and there are rumours that Caesar is calling the shots from a hidden command base in the forest. Enter Harrelson’s Colonel, a cruel special-ops soldier who believes he’s doing the right thing by preserving Earth for humans.

Harrelson, a fan of both the old Planet of the Apes films and the new ones, says he loved the first film in this series. “But the second was even better, and I was waiting with great anticipation to see the third movie, not knowing I would be involved in it,” he says.

From his first day on the Vancouver set, Harrelson said it felt more like “a huge city” because of the enormity of everything there — so many cast members, crew and every kind of camera imaginable. “It was my biggest movie so far; a truly memorable experience for me.”

Much of that positive experience had to do with his fellow filmmakers, like director Matt Reeves (Dawn of the Planet of the Apes, Cloverfield) and the man who plays Caesar, Andy Serkis, whose name has been synonymous with motion-capture acting since he was Gollum in theLord of the Rings films. “I think Matt is an extraordinary director, who has pulled off the impossible with this movie, and Andy is a magical actor. I loved working with them; we had the best time hanging out at my temporary home in Vancouver. Those were great, great times.”

Equally adept at playing funny guys, like the neurotic title character in this past March’s Wilson, and serious characters like the Colonel, Harrelson first endeared himself to audiences as Woody Boyd on TV’s "Cheers" in the late 1980s and early 1990s. He transformed into a film actor with early ’90s movies Doc Hollywood, Indecent Proposal and White Men Can’t Jump, and more recently starred in The Hunger Gamesfranchise and HBO’s "True Detective" alongside his pal Matthew McConaughey.

And for most of these jobs, when he reported for duty, Harrelson brought along an extra staff member.
“I usually have a chef with me on [the] set, because I’m not just vegan; I’m mostly eating raw foods. They’ll often tell me, ‘Here’s some carrot sticks, and here’s some celery. Good luck!’ So it’s better to have someone who is foraging for you.”

While passionate about environmental and food issues, Harrelson understands that preaching rarely works. “I know that it’s very hard to talk somebody out of burgers, if they like burgers. So I don’t really try to do that. But if people ask me, ‘What do I think about dairy?’ I’ll go on a little dissertation. Yes, I will get up on the stump,” he admits.

“Yet, I watch people who are literally eating themselves into an early grave. I just want to say to them, ‘You should not be doing that! Don’t put that in your mouth!’ I’ve seen people literally on their deathbed, but they will not stop eating what they like eating. So that’s like amazing to me.”

There’s no doubt that when it comes to caring for the planet, Harrelson has been in the forefront. He even received an honorary degree from Toronto’s York University for his contributions to environmental education, sustainability and activism.

And maybe it shouldn’t be too surprising to see him playing the chimp-hating Colonel in War for the Planet of the Apes. The franchise is nothing if not a cautionary tale about mankind being pitted against nature and the other creatures on this planet.

In the end, no matter what role he’s playing, Harrelson says he chooses to remain as open-minded as he wants others to be about his concerns for the planet. “It’s important to me to see the rationale for what my character does,” he says, “regardless of whether I am playing man or beast — it’s really all just one wild ride!

Debra Wallace lives in Philadelphia, where she writes about movies and pop culture.